In response to new sanctions against its nuclear program, North Korea says it has canceled its armistice with South Korea and is refusing to answer a hotline phone connected to the South Korean and U.S. militaries. North Korea has threatened a nuclear strike against the South and the U.S. over the sanctions. The North's nuclear tests indicate it can produce some form of nuclear weaponry but may not have mastered the technology to arm a long-range missile with an atomic bomb.